The present invention relates to refractories for casting process which are highly erosion resistant, especially to slag with a high FeO content. These refractories for casting process are effective for the lining of RH type, DH type and other vacuum degassing furnaces where slag with a high FeO content exists, and can also be used as refractories for converters, ladles, torpedo cars, gas blowing lances, etc.
RH type, DH type and other vacuum degassing furnaces are known as molten steel processors. Magnesia-chromite direct bonded bricks have principally been used as lining materials for such vacuum degassing furnaces to date, however, the inherent problems are that burning the brick requires considerable energy and that the construction of the furnaces requires special skill and is very labor-intensive.
In addition, due to the chrome content of magnesia-chromite direct bonded bricks, a problem concerning environmental protection exists as to suitable brick disposal methods after use. Lining vacuum degassing furnaces with monolithic refractories overcomes the high labor and environmental costs otherwise generated in operating such furnaces.
In the operation of vacuum degassing furnaces, however, molten steel and slag are vigorously stirred inside, causing considerable wear of the lining materials. Bricks other than the direct bonded magnesia-chromite types are of insufficient durability and monolithic refractories are far less durable.
Refractories for casting process containing alumina-spinel have been proposed as monolithic refractories for the lining of molten steel vessels. For example, Japanese Provisional Patent publication No. 50-60985 discloses a material containing at least 60 wt % spinel, 10 to 35 wt % alumina and 3 to 10 wt % alumina cement. Japanese Provisional Patent Publication No. 1-87577 discloses another material composed of 50 to 90 wt % alumina, 10 to 40 wt % spinel and 3 to 25 wt % alumina cement. Also, Japanese Provisional patent No. 53-218585 discloses a refractory for casting process having fine magnesia and ultra-fine alumina powder arranged in the matrix section of an alumina material.
These refractories for casting process are highly durable due to the synergistic effect of the erosion resistance of alumina and the slag penetration-proof property of spinel and cause no pollution problem because they contain no chrome.
However, these conventional alumina-spinel or alumina-magnesia refractories for casting process are used only for the lining of molten steel ladles or blast furnace troughs, and are not sufficiently durable for the severe working conditions of vacuum degassing furnaces and, as a result, have not been put to practical use for such a purpose.
In the case of vacuum degassing furnaces, slag has a high FeO content as compared with other molten steel vessels. In conventional refractories for casting process which use alumina cement as the binder, Al.sub.2 O.sub.3 from aggregates and CaO from cement react with FeO present in the slag and produce substances of low-melting point such as Al.sub.2 O.sub.3 -FeO or Al.sub.2 O.sub.3 -FeO-CaO. In the case of vacuum degassing furnaces, one of the major causes of lower lining erosion resistance is that slag has a high FeO content which causes substances of low-melting point to be produced.